omethoate and cyhalothrin did not affect
the S. cerevisiae growth significantly. In triadimefon-treated test,
the cell growth was obviously inhibited at early growth stage, and
the biomass decreased by 12e20% during fermentation. However,
the final biomass concentration did not change significantly
compared with the control group (12.57 versus 12.21 g L1
).
Chlorothalonil inhibited growth of S. cerevisiae more significantly
than the other pesticides. The biomass in treated group decreased
by 69.90% and 12.37% compared with the control test at 32 h and at
the end of fermentation, respectively. Fig. 1B shows the changes in
reducing sugar concentration during fermentation. At the initial
stage, the concentration increased in all of the groups especially in
chlorothalonil-treated test because the added sucrose was hydrolyzed
into reducing sugars by yeast and the slurry itself (Peynaud,
1984). Then the concentration of reducing sugar in each group
decreased rapidly and was almost exhausted except in the
chlorothalonil-treated sample where 63.48 g L1 reducing sugar
still remained in the broth eventually. Fig. 1C shows that the curve
of produced alcohol in chlorothalonil-treated sample was different
from those of other samples. The fermentation was obviously
inhibited in fermentation system containing 0.1 g L1 chlorothalonil,
and only 39.66 g L1 ethanol was harvested after
fermentation. However, no evident difference was found among
the other three pesticide-treated groups and the control group, the
ethanol concentration reached 98.99 g L1 in the broth. On the
other hand, omethoate weakly stimulated the alcohol production
by S. cerevisiae. The phenomenon was not surprising as many reports
had revealed the similar results (Cabras & Angioni, 2000;
Cabras et al., 1999).